A lahar at New Zealand's Mount Ruapehu is all but over, without causing anywhere the level of havoc for which authorities were prepared.

The event was first confirmed by a 3 News helicopter, and then the Department of Conservation.

The Department of Conservation had said that a "moderate lahar" was moving down the side of Mount Ruapehu.

The lahar travelled down the Whangaehu Valley, past the Tongariro catchment; and then continued on to the Tangiwai Bridge, the site of the 1953 Tangiwai disaster, which was itself caused by a lahar.

The crater lake is currently being reported by a free phone number as at a warning level of 3a. The crater lake is also being reported at a level between 5.7-6.7 metres up the Crater Lake tephra dam.

The lahar emergency plan was activated by Civil Defence. The district mayor of Ruapehu, Sue Morris, and conservation minister, Chris Carter, said that the authorities had been very quick to respond to the emergency. All three electronic surveillance technologies had their alarms activated. Mr Carter said, "The lahar travelled down the path as predicted, and the early warning response system that this government provided worked exactly as planned."

Highways near Mount Ruapehu were closed by the Ohakune police, including the Desert Road. The roads have now been re-opened.

A lahar has been expected for a long time now, and scientists say the lahar could have been caused by, among other things, the bad weather New Zealand has been having lately.

Since 1996 the water level in the crater lake at the top of Mount Ruapehu has been rising, which created a risk of a lahar last year.